Radiofrequency (RF) energy is delivered to a surgical instrument, such as a probe, to treat diseased tissue, such as by ablating, shrinking, cutting, or coagulating the tissue. For example, RF energy is used to ablate fibrillations and smooth the surface of articular cartilage that suffers from chondromalacia and osteoarthritis. RF energy also is used to shrink collagen tissue in a joint. The use of RF energy can produce collateral damage in the form of undesired cell death or the excess removal of healthy tissue. For example, in the case of articular cartilage, RF energy can cause the death of chondrocytes, the cells responsible for maintaining cartilage viability and growth, which cannot be regenerated after death.